The invention relates to a method for operating a spark-ignition internal combustion engine having a combustion chamber, a fuel injector arranged in the combustion chamber and an ignition source for igniting a fuel/air mix formed in the combustion chamber, part of the fuel quantity which is introduced into the combustion chamber being injected as a pre-injection during an intake stroke of the internal combustion engine.
During a startup phase of a spark-ignition internal combustion engine with direct injection of fuel, the internal combustion engine, following a cold start, is operated with a rich charge mix to ensure sufficient reliability of ignition of a mix formed in the combustion chamber and to heat a catalytic converter device provided for the exhaust gas treatment. This also allows the internal combustion engine to run more smoothly.
With the previously known methods for heating up an exhaust-gas catalytic converter for a direct injection spark-ignition engine, the heat-up phase of the exhaust-gas catalytic converter which is required until a light-off temperature of the exhaust gas catalytic converter is reached during cold-start operation is too long. The light-off temperature is the temperature or temperature range at or in which a significant conversion rate is achieved by the catalytic converter, e.g. between 20% and 50%, i.e. when significant conversion of hydrocarbons, carbon monoxide and nitrogen oxides begins.
It is the object of the invention to provide a method for operating the internal combustion engine in such a manner that an exhaust-gas catalytic converter of the internal combustion engine is heated up rapidly during a cold-start phase.